Method of galvanizing



March 27, c; K

METHOD OF GALVANIZING 2 Sheets-Sheet 1 Filed Aug. 28, 1947 Mama C (W5,

. O T T A 5 H Patented Mar. 27, 1951 2,546,451 METHOD OF GALVANIZING Michael C. King, Pittsburgh, Pa., assignor to United States Steel Company, a corporation of New Jersey Application August28, 1947, Serial No. 771,066

- .ZyClaim s. 1

This invention relates to an improved method and apparatus for hot-dip galvanizing steel strip and the like.

Present day methods of applying molten zinc to ferrous metal sheets to obtain good bonds therebetween involve, as a rule, treatments of the sheet or strip surface to obtain thereon a layer of substantially pure iron. I have determined, however, that the obtaining of such a layer is unnecessary if certain steps hereinafter disclosed for preparing the metal surface are followed. By so doing, the expensive and intricate. practices of' the'prior art are avoided and, at. the same time, better bonded coatings are .obtained.

I have discovered that superior coating adherenceas well as improved performance of the hot-dip galvanizing pots, is obtained by passing the strip'or sheets through a bath of. palm oil, Hydrofol, a hydrogenated fish oil or oleic acid, which is in contact with the molten spelter. It has heretofore been impossible to have palm oil and the like in direct contact with the molten zinc spelter, since the conventional 790 to 850 F. temperature of the spelter exceeds the flash point of such material.

It is accordingly an object of the present in-. vention to provide an-improved method and apparatus for galvanizing ferrous metal sheets and strip.

It is a further object to provide a method and apparatus for maintaining an entry bath of palm oil and the like in contact with the molten zinc spelter bath for hot-dip galvanizing ferrous metal sheets and strip.

The foregoing and further objects will become apparent from the following specification when read in conjunction with wherein:

Figure 1 is a side elevation partly in section;

Figure 2' is ,anenlarged detail of the cleaning tank;.and

,.Figure 3 is an enlarged detail of the ing pot;

' Referring more particularly to the drawings, the letter C designates a coil of ferrous strip material which has preferably been box annealed in a reducing atmosphere at a temperature between 1200 F. and 1300 F. The annealed coil C is mounted on an uncoiler 2 which feeds the strip into an electrolytic pickling tank 4 provided with electrodes 6 and guide rolls 8. The electrolyte used in the tank is preferably a 15 aqueous solution of hydrochloric acid held at a temperature between 90 and 120 F.

Disposed adjacent to and in longitudinal align sal a the attached drawings,

ment with the pickling tank 4 is a water rinse tank l0 having a partially submerged roller 12 at its mid-portion for maintaining the strip below the surface of the water in the tank. At the outlet end of the water tank are squeegee rolls l4 adjusted to remove most of the rinse water from the advancing strip.

In longitudinal alignment but somewhat spaced from the rinse tank I0 is a hotdip galvanizing pot l6 containing a bath of molten zinc spelter having conventional commercial purity or a1- loyed' with effective small percentages ofztin, antimony or aluminum and maintained at sube stantially a level; indicated by the dotted line aa. The pot is provided with submergedzinlet guide rolls I8, a lower submerged guide roll 20 and partially submerged outlets'queegee rolls 22. As the strip leaves the pot, it travels upwardly over a guide roll 24 and downwardly to a coiler' 26'.

In accordance with the teachings of my inven-.

'tion, there is providedabove the pot 16 a box-like container 30 for palm oil and the like. The for-'- ward end 32 of the container extends to ap'proxi mately the mid-portion of the pot whereas the rearward end 34 extends outwardly from thepot towards the rinse tank ID. A guide roll 36 is provided above the rearward end 34'and sub merged guide rollers 38 and 40 are provided'in the container adj aeent the rearward and forward ends respectively. The strip is adapted to travel over rolls 35-and 40 and under roll 38. On the bottom of the forward end of the conf tainer 30, there is provided a downwardly depending elongated narrow spout member 42 which extends to a point adjacent the guide rolls"!!! and below the level of the molten spelter. This slot-like guide member 42 extends across sub stantially the width of'the container 30 so as to receive the widest strip passed therethrough'.

From this, it "is seen that the palm oil or other material inthe container is maintained incon-v tact with the molten spelter-so that the strip. is encased in the-palm oil'bath until it enters the: zinc plating bath. J .f

The palm oil bath has a double function of driving off from the stock passing through it the remains of pickling acid and rinse water left on it by squeegee rolls 8 and then preparing the surface of the stock for the reception of zins coating. The container 30 is designed to provide an adequate cooling of the palm oil or an equivalent substance therein. In many cases, it is possible to achieve the desired lowering of the temperature by natural heat radiation in atmosphere by reason of tank 30 having sufficiently 3 large dimensions in proportion to the surface area of spout 42. Since heat is supplied to the tank 30 principally by radiation and convection from galvanizing pot I 6, a proper adjustment of supply of heat to the oil may be achieved, when so desired, by partial heat insulation of tank 30 on the sides receiving heat from galvanizing pot H5, or by complete heat insulation of them using only moderately elficient insulating material. In some cases, a burner 44 may be provided for heating tank 30 independently of galvanizing pot l6.

A total prevention of heat access stances, is predicated on maintaining it at an to tank 30 I is neither intended nor desiredysince proper functioning of palm oil and of equivalent subelevated temperature in the range of.,300 1133,350

F. and preferably at 325 F. 'Heat radiatedf'rom galvanizing pot l6 provides this heating effect fect of molten zinc. accumulates in spout 42 where it comes incontact with the heated walls thereof. Heated oil then risesi into tank 39 thus assisting circulation necessary for keeping oil temperature at a predetermined level; Most average operating conditions do not require forced circulation, but, when requir thi forced circulation can be provided by many methods familiar to those skilled in the art.-

: If desired, the conventional flux box 43 can-be retained on the pot to vform a erme i .Q m r 4i and thereby reduce oxidation of the Surface of the molten zinc adjacent the str p-in t- I {It has been discovered that, once properly l an s ip is treated by the application of hot palm oil and the like, further galvanizin operations can be conducted in aconventional manner. provided the original imm rsi n o t el base into molten spelter is c ec h ugh an oil sea-l as described above. I In the preferred manner of producing the present invention for making tight-coated galvanized steel, low-carbon commo t e i ot are reduced to strip of the desired gage in conventional manner, coiled, and the coils are annealed under cover at substantially l200 to 1300 F. in a reducin atmosphere, exemplified by as containing 4 to 6% E02, 9% C 10% 1- 2,

the rest being nitrogen. After cooling to subvice and having an average temperature of substantially soo to 350 E. 325 F. bein p efe able. The strip is then passed into the galvanizing not containing spelter alloyed with 0.12 to 0.25% aluminum and maintained at a temperae 4 ture of 820 to 830 F. On leaving the pot, the coated strip is allowed to cool in still or agitated air, depending on the character of spangle desired, while passing to roll 24 and then to coiler 26. I

Galvanized strip made according to the method of the present invention has coating adherence characteristics superior to those encountered in commercial hot-dipped product having so-called tight-coat characteristics. The method further provides an efficient and economical means for converting conventional galvanizing lines into equipment suitable for manufacturing highP-grade galvanized steel.

1 stood that this embodment is merely for the purpose of illustration and description and that various other forms may be devised within the scope of my invention, as defined in the appended claims. 1

'I claim:

1. A method of producing a galvanized ferrous metal body by immersing said body in a bath of molten zinc comprising passing said body through a bath. of palm oil, nd then n n through .a molten zinc bath, said palm oil bath being disposed a substantial distance above the molten zinc bath, said palm oil bath being connected tothe zinc .bathby a narrow spout-like column of palm oil extending downwardly from said palm oil bath onto said molten Zinc b h,- the thickness of said colulnli'being verylittle in excess of the thickness of the artiQlepassed therethrough.

2. A method of producin a galvanized ierrous metal body by mm rs ng s id. body ina bathvof molten zinc comprisin passin said bo y thro gh a bath of; palm oil andthen into an through a molten zinc bath, said palm oil bath being maintained at a temperature between 300, and 350 F. and being disposed a substantial distance above the molten zinc bath, said palmoil bath being connected to the zinc bath by a narrow spout-like column of palm oil extending downwardly from said palm oil bath onto said molten zinc bath, the thi kness of said colu n being very little in excess of the thickness of the article passed therethrough.

7 MICHAEL 0. KING.

nnrnnnuors CITED The following references are of record in th file of this patent:

UNITED snares PATENTS Number Name Date ,223,355 Gonser wt-"w," Dec. 3, 1-940 FOREIGN PATENTS Number Country Date 1,901 Great Britain .185; 21,1191 GreatBrita-in ,.M.. .1891 

1. A METHOD OF PRODUCING A GLVANIZED FERROUS METAL BODY BY IMMERSING SAID BODY IN A BATH OF MOLTEN ZINC COMPRISING PASSING SAID BODY THROUGH A BATH OF PALM OIL AND THEN INTO AND THROUGH A MOLTEN ZINC BATH, SAID PALM OIL BATH BEING DISPOSED A SUBSTANTIAL DISTANCE ABOVE THE MOLTEN ZINC BATH, SAID PALM OIL BATH BEING CONNECTED TO THE ZINC BATH BY A NARROW SPOUT-LIKE COLUMN OF PALM OIL EXTENDING DOWNWARDLY FROM SAID PALM OIL BATH ONTO SAID MOLTEN ZINC BATH, THE THICKNESS OF SAID COLUMN BEING VERY LITTLE IN EXCESS OF THE THICKNESS OF THE ARTICLE PASSED THERETHROUGH. 